The FAA has released its report about factors that may have led to several in-flight structural failures of the Zodiac CH601XL in the United States and abroad.

The agency issued a special airworthiness information bulletin for existing Zodiacs and suspended the issuance of any new airworthiness certificates to variants of the Zodiac CH601XL and CH650 after a fatal accident in November, the fifth in-flight structural failure of a CH601XL in the United States since 2005. The agency has now released a special review of the CH601XL and CH650, which are nearly identical; the report concludes that the investigation did not indicate a single root cause. Instead the investigation implicated the potential combination of several design and operational aspects, one of which is that the wing loads used to design the Zodiac CH601XL did not meet ASTM standards—the standards used for light sport aircraft—for a 1,320-lb airplane. During its review, the FAA also identified issues with other factors such as flutter, improper airspeed calibration, stick forces, and structural stability.

The report was a continuation of an FAA review started in 2006. The FAA estimates that the wing design loads were 20 to 25 percent too low for the certified maximum takeoff weight and recommends that operators not fly the aircraft until a manufacturer’s fix can be installed. Other recommendations include changes to the ASTM standards to address other contributing factors.

The aircraft in question are available as special light sport category aircraft (S-LSA) from Aircraft Manufacturing and Design Inc. (AMD) or as amateur-built kits from Zenith Aircraft. Owners of S-LSAs must comply with the manufacturer’s safety directive, and AOPA strongly urges pilots not to fly any of the CH601XL or CH650 aircraft in the S-LSA and experimental amateur-built categories until they have complied with the directive.

Zenith comments on FAA report

Sebastian Heintz, president of Zenith Aircraft, speaking only for the amateur-built Zodiac kits, said there is little new in the FAA’s report. He is shipping modification kits that meet FAA concerns.

“There’s really no news in the report,” he said. He noted that one of the recommendations in the report calls for making the modifications already offered. The report did, however, call for additional testing. He is trying to determine what the FAA wants in terms of additional testing.